1. Field of the Invention
The present invention relates to an inline detection device for defects in semiconductor devices, and more particularly to an inline detection device for self-aligned contact defects.
2. Description of the Prior Art
In the continuous development of integrated circuits (IC) of higher density and chips in reduced size, misalignment of various layers is a major issue. Consequently, the self-aligned contact (SAC) process has evolved to reduce the distance between elements and increase the density of elements.
However, the tolerance for defects is reduced greatly as a consequence of reduced IC size and higher density. Therefore, defects must be improved to increase yield. The lower the defect density, the higher the yield. In order to detect defects in ICs, various tests are usually conducted at specific stages.
At the moment, the self-aligned contact process is conducted by etching between gates with the protection of spacers to avoid overetching. Thus, if the spacers are overetched, causing shorts, the performance of the products is severely affected and the yield is lowered. Conventional detection of defects is conducted after the formation of metal lines. According to the prior art, not only can the defects not be detected immediately following the formation of self-aligned contacts, needless waste of material and process time cannot be avoided. Therefore, the conventional detection method is far from ideal.
Another object of the present invention is to provide a method for fabricating an inline detection device for self-aligned contact defects utilizing general processes to form the inline detection device simultaneously with the semiconductor device without extra process steps.
Another object of the present invention is to provide an inline detection device having high sensitivity and increased detection efficiency to precisely detect defects in self-aligned contact/gates.
To achieve the above-mentioned objects, the present invention provides an inline detection device formed in a semiconductor substrate for self-aligned gate defects; the device comprising: an active area, formed on the semiconductor substrate, which is comprised of a serpentine gate, at a plurality of first contact window, nested immediately between the same spacer, a plurality of first contact plugs formed in the first contact windows, and two probing pads, formed in the semiconductor substrate, which is comprised of a plurality of matrix gates, a second contact windows exposing portions of the matrix gates, and a second contact plug formed in the second contact window.
According to the present invention, the method for fabricating an inline detection device for self-aligned contact defects comprises:
(a) providing a semiconductor substrate having an active area and two probing pad;
(b) forming a serpentine gate over the active area, wherein the serpentine gate divides the active area into two electrically disconnected areas connecting respectively with the two probing pads;
(c) forming a plurality of matrix gates over the two probing pads;
(d) forming spacers on two side of the serpentine gate;
(e) forming a plurality of first contact windows nesting immediately between the same spacer on the active area and forming a second contact window exposing portions of the matrix gates; and
(f) forming a plurality of first contact plugs and a second contact plug in the first contact windows and the second contact window respectively; wherein each of the first contact plugs is for contacting with one of the two electrically disconnected areas of the active area.
In the inline detection device for self-aligned contact defects of the invention, the shape of the matrix gates is not limited, square or circular shapes used in the prior art can be adopted. Also, the pattern of the matrix gates are not limited, it can be distributed as a matrix.
In terms of material, the first contact plugs and the second contact plug are either tungsten or polysilicon. The spacer is dielectric material, such as silicon nitride.
The inline detection device for self-aligned contact defects of the invention is show in FIG. 1A, wherein the active area 10 having a serpentine gate 30 and a plurality of first contact windows 20 is divided into two parts by the serpentine gate 30. Two sides of the active area 10 are connected with probing pads 40, 50 respectively. In the probing pads 40 and 50, there are a second contact window 60 and a plurality of matrix gates 70 located at the bottom of the second contact window 60. The pattern of the serpentine gate 30 in tho active area 10 is not limited, as long as the serpentine gate divides the active area into two parts and they are not electrically connected. That is, the pattern shown in FIG. 1B can be adopted as well.
FIG. 2 is a cross-section of FIG. 1A along the line B-Bxe2x80x2. In FIG. 2, 100 represents the semiconductor substrate of the active area, and 103 represents oxide. The plurality of the first contact windows 20 are nested immediately between the same spacer of the serpentine gate 101, wherein spacers 102 are formed on two sides of the first gate 101. In addition, the area outside of the active area AA is a first contact region 110 formed by ion implantation, and first contact plugs 105 fill the first contact windows 20.
FIG. 3 is a cross-section along the line C-Cxe2x80x2 in FIG. 1A. In FIG. 3, 200 represents the probing pads, 203 represents oxide, 60 represents the second contact window in FIG. 1, 201 represents plurality of the matrix gates formed at the bottom of the second contact window 60, 202 represents the spacers formed on the sides of the matrix gates 201, and 210 represents a second contact region formed by ion implantation outside the area of the matrix gates 201. In addition, the second contact window 60 is filled by a second contact plug 204. The plurality of matrix gates are used to prevent damage caused by plasma when etching contact windows and to avoid not filling the contact windows completely because of the larger size of the contact windows. Moreover, when taking electrical measurements, voltage applied can be distributed evenly throughout the probing pads.
The number and the shape of the matrix gates in the probing pads are not restricted and can be adjusted based on the number of the serpentine gate in the active area and the process conditions. However, in order to integrate the process, it is advantageous to have identical width for the serpentine gate and the matrix gate.
According to the detection device of the invention, the active area is divided into two electrically disconnected areas by the serpentine gate. Each of the first contact plugs is for contacting with one of the two electrically disconnected areas of the active area. Hence, if over etching occurs in the formation of the self-aligned contact, shorts will occur. In this circumstance, by applying the two probing pads to ground connection and a certain voltage respectively, defects in the active area will be detected.